When conducting well operations, situations arise where objects must be retrieved from the wellbore. This can occur when casing or tubing experiences a catastrophic failure and a portion of the casing or tubing string falls to the bottom of the wellbore. The segment that has fallen into the bottom of the wellbore needs to be removed so that further operations can continue. Alternatively, certain kinds of tools used in drilling or workover operations may become stuck in the wellbore and may require retrieval with a tool such as a spear or an overshot.
In the past, various mechanical designs have been employed for such tools primarily involving a series of mechanically actuated grippers or slips to grab the object to be retrieved, or "fish," so that it can be brought to the surface. Typically, these designs have involved shear pins that must bee sheared to allow release from the fish if necessary. These tools are not resettable once the shear pin has been broken. The use of shear pins further limits the operational use of such tools in limiting the maximum upward pull that can be exerted. Pulling operations with tools that are released via a shear pin have to be carefully done to avoid inadvertent releases. Additionally, use of such tools even without shearing the pin can, due to the cyclical stresses imposed on shear pins weaken them so that they may fail under pulling forces smaller than normally anticipated.
Various tools in the past have employed different mechanisms to set the slips. Some have done so mechanically while others have done so hydraulically. Typical of such tools are U.S. Pat. Nos. 808,378 (mechanically set); 803,450 (hydraulically set); 1,457,139 (hydraulically set); 1,728,136 (hydraulically set); 1,619,254 (hydraulically set); 1,580,352 (hydraulically set); 1,621,947 (hydraulically set); 1,638,494 (hydraulically set); 1,712,898 (hydraulically set); 1,779,123; 1,794,652; 1,815,462; 1,917,135; 2,141,987; 2,290,409; 2,806,534; 2,732,901; 3,638,989; and 3,262,501. Some of these tools employ hydraulic force to move a piston to in turn move a mechanical member which in turn sets the slips for gripping. Thereafter, some mechanical action is required to release the slips such as breaking a shear pin by pulling up on the tool with sufficient force.
Also of interest is European Patent Application 0213798 which discloses a packer retrieval assembly. This device presents two different outside diameters so that it can be inserted through a packer and expanded to its larger diameter for retrieving the packer. This apparatus also uses shear pins to actuate from one position to another. U.S. Pat. No. 4,616,721 shows a packer retrieving tool having a milling feature for cutting loose the slips. This tool can disengage the packer only by failure of a ring component from hoop tension. At that point, the packer falls to its original position and the tool must be removed from the well to be reset.
Also of interest to the field of this invention is a packer retrieving tool product no. 646-17 made by Baker Oil Tools and referred to as Baker 43 RETRIEVA-D LOK-SET.RTM. which is used to retrieve Baker 43 RETRIEVA-D LOK-SET.RTM. packers.
The features not found in the prior art which have brought about the development of the apparatus of the present invention are primarily oriented toward a design which readily permits transmission of torque without mechanical damage and an apparatus that can be reset a multiplicity of times due to its dependency on an hydraulic release.